1. Field of the Invention
The present invention relates to current sensing circuits, and in particular, to current sensing circuits which provide for direct, in-line, non-inductive current sensing with low insertion loss.
2. Description of the Related Art
Unlike voltage monitoring, which can be done with a high degree of precision while introducing virtually no losses into the system whose voltage is being monitored, current sensing has required sacrificing precision for low insertion loss or suffering high insertion loss for greater precision. For example, one conventional current sensing technique with low insertion loss requires the use of an inductive sensor which senses current by the presence and strength of a magnetic field surrounding the conductor in which the current is conveyed. While the insertion loss introduced by this technique is very low (assuming negligible effects from interaction between the inductive sensor and the magnetic field generated by the current), a high degree of mechanical precision is required in that the proximity and placement of the inductive sensor must be consistent and carefully calibrated.
A conventional direct, in-line current sensing technique requires the insertion of a resistor in series with the load whose current is to be sensed. However, due to the necessity of having a relatively high voltage across such resistor so as to avoid errors caused by a variety of factors such as noise, such resistor can introduce significant losses due to its own power dissipation. While reducing the resistance will reduce such losses, the voltage generated by the current of interest is also reduced, thereby resulting in increased errors when such low voltages are measured. Such errors include inaccurate voltage readings due to offset voltages in the monitoring circuitry, as well as inaccuracies due to noise and temperature drift of the sensing resistor.
Accordingly, it would be desirable to have a current sensing circuit which allows high precision, in-line current sensing with low insertion loss.